A M_L3.8 earthquake occurred on February 23,2014 in Rongchang County,which is located at the southern edge of the Sichuan Basin in the border area between Sichuan and Chongqing. This paper presents results of focal me...A M_L3.8 earthquake occurred on February 23,2014 in Rongchang County,which is located at the southern edge of the Sichuan Basin in the border area between Sichuan and Chongqing. This paper presents results of focal mechanism solution of this earthquake using the CAP( cut and paste) method based on broadband seismograms recorded by regional seismic stations. Our results show that the moment magnitude is M_W3. 09 and focal depth is 3km. The hypocenter of this earthquake is located close to a buried fault in the Luoguangshan anticline. Oil prospecting and deep drilling data indicate that this buried fault is a thrust fault,striking SW230°,dipping NW45°,and 1. 7km deep. There are some injection wells within the anticline,and significant injection-induced earthquakes were observed during the periods of injection of waste water into the deep formations through those wells. The best double couple solution of the M_L3.8 earthquake is 247°,48°and 104° for strike,dip and rate,respectively,for one nodal plane( and 46°,44° and 74°for another nodal plane),which is in agreement with the geometry of the buried fault.Therefore,we conclude that the M_L3.8 Rongchang earthquake is possibly the result of faulting along the buried reverse fault induced by water injection under the compressive stress regime in the area.展开更多
Based on data collected from a temporal seismic network, and in addition to the data from some nearby permanent stations, we investigate the velocity structure and seismicity in the Rongchang gas field, where signific...Based on data collected from a temporal seismic network, and in addition to the data from some nearby permanent stations, we investigate the velocity structure and seismicity in the Rongchang gas field, where significant injection-induced seismicity has been identified. First, we use receiver functions from distant earthquakes to invert detailed 1-D velocity structures beneath typical stations. Then, we use the double-difference hypocenter location method to re-locate earthquakes of the 2010 MLS. 1 earthquake sequence that occurred in the region. The re-located hypocenters show that the 2010 MLS. 1 earthquake sequence was distributed in a small area surrounding major injection wells and clustered mostly along pre-existing faults. Major earthquakes show a focal depth less than 5km with a dominant depth of -2km, a depth of major reservoirs and injection wells. We thus conclude that the 2010 ML 5. 1 earthquake sequence might have been induced by the deep well injection of unwanted water at a depth - 3km in the Rongchang gas field.展开更多
We use five published source models to calculate the Coulomb failure stress changes induced by the Ms8.0 Wenchuan earthquake, and analyze the association between stress changes and the subsequent earthquakes. Based on...We use five published source models to calculate the Coulomb failure stress changes induced by the Ms8.0 Wenchuan earthquake, and analyze the association between stress changes and the subsequent earthquakes. Based on the analysis of uncertainties resulting from source models, we determine the stress changes on nearby faults caused by the Wenchuan earthquake. Moreover, we focus on the seismicity rate change as a function of time on every fault under the influence of stress changes. The results indicate that the spatial distributions of aftershocks correlate well with the regions where stress is calculated to increase using the related models. The largest lobes of dropped stress lie in the west and east sides of source fault. The largest lobes of increased failure stress close to southern and northern ends of the source fault extend into the whole source failure plane. In addition, another region of increased stress lies in the Wenchuan-Yingxiu zone close to the southern segment of source fault, where a large number of aftershocks have occurred. And subsequent earthquakes seem to extend to even more remote distances; therefore, this area also has a high risk of seismic hazard. We find that the positive stress changes on nearby faults imposed by the Wenchuan earthquake produce an encouraging effect on seismicity rate. The effect is most significant on the Pengxian-Guanxian fault and Qingchuan fault, the value of seismicity rate maintains two times greater than the value before the mainshock for the next hundred years on these faults, and the time needed for the aftershock rate to recover to the pre-mainshock seismicity rate can reach up to 800-900 yr. The influence is not significant on the western Qinling fault, the Longquanshan fault, the Xianshuihe fault, the Yulongxi fault, the Anninghe fault, the Minjiang fault, and the Aba fault. Compared with the seismicity rate on these faults before the mainshock, the aftershock rate is raised by less than two times, and the time of perturbation duration is not long. The stress changes on the Fubianhe fault and Huya fault are negative, which reduce the seismicity for the next thousand years. Under the influence of stress changes caused by the Wenchuan earthquake, both Pengxian-Guanxian fault and Qingchuan fault have a high risk of earthquake occurrence.展开更多
Based on calculations of the tidal Coulomb failure stress and investigations of the correlation between the Earth tide and the Ning＇er earthquake sequence, the processes of fault nucleation and failure were simulated...Based on calculations of the tidal Coulomb failure stress and investigations of the correlation between the Earth tide and the Ning＇er earthquake sequence, the processes of fault nucleation and failure were simulated. In these simulations we consider the influence of tidal stresses using the rate- and state-dependent friction laws. Furthermore, the effects on tidal trig- gering due to the stress amplitude and periodic oscillation properties were investigated, and the triggering effects between the tidal normal and tidal shear stresses were compared. The results showed that the Ning＇er earthquake sequence was a physical consequence of tidal effects. A transition period To exists between the nucleation and failure processes of a seismic fault. When the period T of stress is equal to or becomes larger than To, the fault response becomes dependent on the periodic features of the loading stress; however, for T 〈 To, the response of the fault is nearly independent of the period. Both the tidal normal and tidal shear stresses have similar effect in the nucleation and failure processes; the clock changes generally increase with the maximum amplitudes of the tidal stresses. Tidal normal and tidal shear stresses with positive amplitudes mainly induce earth- quake triggering; however, the triggering effects induced by negative tidal stresses are smaller and faults are not sensitive to negative tidal stresses. Our results primarily reveal the physical mechanisms of tidal stress triggering.展开更多
基金funded jointly by the Scitech R&D Program of Chongqing Municipality(cstc2014yykfA00002(cstc2014yykfA0234),cstc2014jccxA0028 and cstc2013ggB0011)the Spark Program of Earthquake Sciences of CEA(Grant No.XH14042)
文摘A M_L3.8 earthquake occurred on February 23,2014 in Rongchang County,which is located at the southern edge of the Sichuan Basin in the border area between Sichuan and Chongqing. This paper presents results of focal mechanism solution of this earthquake using the CAP( cut and paste) method based on broadband seismograms recorded by regional seismic stations. Our results show that the moment magnitude is M_W3. 09 and focal depth is 3km. The hypocenter of this earthquake is located close to a buried fault in the Luoguangshan anticline. Oil prospecting and deep drilling data indicate that this buried fault is a thrust fault,striking SW230°,dipping NW45°,and 1. 7km deep. There are some injection wells within the anticline,and significant injection-induced earthquakes were observed during the periods of injection of waste water into the deep formations through those wells. The best double couple solution of the M_L3.8 earthquake is 247°,48°and 104° for strike,dip and rate,respectively,for one nodal plane( and 46°,44° and 74°for another nodal plane),which is in agreement with the geometry of the buried fault.Therefore,we conclude that the M_L3.8 Rongchang earthquake is possibly the result of faulting along the buried reverse fault induced by water injection under the compressive stress regime in the area.
基金supported by the grants of Spark Program of China Earthquake Administration ( XH12038Y )the State Key Laboratory of Earthquake Dynamic( LED2008B04)+1 种基金Science and Technology Program of Chongqing Municipality in 2011 (Grant No. CSTC,2011AC0149)Research on the New Pattern and Key Techniques of the Earthquake Emergency Decision in Southwest China (201108013)
文摘Based on data collected from a temporal seismic network, and in addition to the data from some nearby permanent stations, we investigate the velocity structure and seismicity in the Rongchang gas field, where significant injection-induced seismicity has been identified. First, we use receiver functions from distant earthquakes to invert detailed 1-D velocity structures beneath typical stations. Then, we use the double-difference hypocenter location method to re-locate earthquakes of the 2010 MLS. 1 earthquake sequence that occurred in the region. The re-located hypocenters show that the 2010 MLS. 1 earthquake sequence was distributed in a small area surrounding major injection wells and clustered mostly along pre-existing faults. Major earthquakes show a focal depth less than 5km with a dominant depth of -2km, a depth of major reservoirs and injection wells. We thus conclude that the 2010 ML 5. 1 earthquake sequence might have been induced by the deep well injection of unwanted water at a depth - 3km in the Rongchang gas field.
基金supported by National Natural Science Founda-tion of China (Grant No. 40364001)the Construction Project of Inte-grated Deep-Well Seismic Observation System in Shanghai
文摘We use five published source models to calculate the Coulomb failure stress changes induced by the Ms8.0 Wenchuan earthquake, and analyze the association between stress changes and the subsequent earthquakes. Based on the analysis of uncertainties resulting from source models, we determine the stress changes on nearby faults caused by the Wenchuan earthquake. Moreover, we focus on the seismicity rate change as a function of time on every fault under the influence of stress changes. The results indicate that the spatial distributions of aftershocks correlate well with the regions where stress is calculated to increase using the related models. The largest lobes of dropped stress lie in the west and east sides of source fault. The largest lobes of increased failure stress close to southern and northern ends of the source fault extend into the whole source failure plane. In addition, another region of increased stress lies in the Wenchuan-Yingxiu zone close to the southern segment of source fault, where a large number of aftershocks have occurred. And subsequent earthquakes seem to extend to even more remote distances; therefore, this area also has a high risk of seismic hazard. We find that the positive stress changes on nearby faults imposed by the Wenchuan earthquake produce an encouraging effect on seismicity rate. The effect is most significant on the Pengxian-Guanxian fault and Qingchuan fault, the value of seismicity rate maintains two times greater than the value before the mainshock for the next hundred years on these faults, and the time needed for the aftershock rate to recover to the pre-mainshock seismicity rate can reach up to 800-900 yr. The influence is not significant on the western Qinling fault, the Longquanshan fault, the Xianshuihe fault, the Yulongxi fault, the Anninghe fault, the Minjiang fault, and the Aba fault. Compared with the seismicity rate on these faults before the mainshock, the aftershock rate is raised by less than two times, and the time of perturbation duration is not long. The stress changes on the Fubianhe fault and Huya fault are negative, which reduce the seismicity for the next thousand years. Under the influence of stress changes caused by the Wenchuan earthquake, both Pengxian-Guanxian fault and Qingchuan fault have a high risk of earthquake occurrence.
基金supported by the National Natural Science Foundation of China(Grant Nos.4110403641004021)+1 种基金Foundation of Provincial Education Department of Yunnan(Grant No.2014Z009)Foundation of School of Resources&Earth Science in Yunnan University(Grant No.2013CK002)
文摘Based on calculations of the tidal Coulomb failure stress and investigations of the correlation between the Earth tide and the Ning＇er earthquake sequence, the processes of fault nucleation and failure were simulated. In these simulations we consider the influence of tidal stresses using the rate- and state-dependent friction laws. Furthermore, the effects on tidal trig- gering due to the stress amplitude and periodic oscillation properties were investigated, and the triggering effects between the tidal normal and tidal shear stresses were compared. The results showed that the Ning＇er earthquake sequence was a physical consequence of tidal effects. A transition period To exists between the nucleation and failure processes of a seismic fault. When the period T of stress is equal to or becomes larger than To, the fault response becomes dependent on the periodic features of the loading stress; however, for T 〈 To, the response of the fault is nearly independent of the period. Both the tidal normal and tidal shear stresses have similar effect in the nucleation and failure processes; the clock changes generally increase with the maximum amplitudes of the tidal stresses. Tidal normal and tidal shear stresses with positive amplitudes mainly induce earth- quake triggering; however, the triggering effects induced by negative tidal stresses are smaller and faults are not sensitive to negative tidal stresses. Our results primarily reveal the physical mechanisms of tidal stress triggering.
